U.S. patent number 6,037,691 [Application Number 09/236,250] was granted by the patent office on 2000-03-14 for dual excitation electrical machine, and especially motor vehicle alternator.
This patent grant is currently assigned to Valeo Equipments Electriques Motoer. Invention is credited to Dokou Antoine Akemakou.
United States Patent |
6,037,691 |
Akemakou |
March 14, 2000 |
**Please see images for:
( Certificate of Correction ) ** |
Dual excitation electrical machine, and especially motor vehicle
alternator
Abstract
A flux commutating electrical machine includes a stator and a
rotor, the stator including at least one armature coil housed in at
least one pair of notches and the rotor selectively establishing
closed magnetic circuits around sections of the armature coil(s).
At least one excitation permanent magnet establishes a magnetic
flux in a circumferential direction of the rotor and at least one
excitation coil establishes a localized variable magnetic flux in
the same circumferential direction as the flux produced by the
magnet(s). The magnet or each magnet is housed in a first rotor
part defining a first pair of rotor poles, the coil is or the coils
are housed in a second rotor part defining a second pair of rotor
poles and the rotor parts are separated from each other by
essentially magnetically non-conductive areas.
Inventors: |
Akemakou; Dokou Antoine (Vitry
sur Seine, FR) |
Assignee: |
Valeo Equipments Electriques
Motoer (Creteil, FR)
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Family
ID: |
9522146 |
Appl.
No.: |
09/236,250 |
Filed: |
January 25, 1999 |
Foreign Application Priority Data
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Jan 26, 1998 [FR] |
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98 00781 |
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Current U.S.
Class: |
310/191; 310/114;
310/156.55; 310/174; 310/179; 310/216.069 |
Current CPC
Class: |
H02K
21/042 (20130101) |
Current International
Class: |
H02K
1/22 (20060101); H02K 21/04 (20060101); H02K
21/00 (20060101); H02K 001/00 () |
Field of
Search: |
;310/191,261,156,174,179,114 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 707 374 A1 |
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Apr 1996 |
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EP |
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41 39 843 |
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Jun 1993 |
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DE |
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96 30992 |
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Oct 1996 |
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WO |
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Other References
English Abstract (Derwent) of European Patent Application No. EP 0
707 374 A1 to J. Lucidarme et al. (Apr.17, 1996). .
Patent Abtstracts of Japan, vol. 018, No. 109 (E-1513), Feb. 22,
1994 & JP 05 304752 A (Fuji Elelctric Co Ltd), Nov. 16, 1993.
.
French Search Report dated Oct.23, 1998..
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Primary Examiner: Ramirez; Nestor
Assistant Examiner: Lam; Thanh
Attorney, Agent or Firm: Morgan & Finnegan, LLP
Claims
What is claimed is:
1. A flux commutating electrical machine comprising:
a stator including at least one armature coil housed in at least
one pair of notches; and
a rotor including means for selectively establishing closed
magnetic circuits around sections of said armature coil, said means
for selectively establishing including at least one excitation
permanent magnet adapted to establish a magnetic flux in a
circumferential direction of said rotor and at least one excitation
coil adapted to establish a localized variable magnetic flux in the
same circumferential direction as the flux produced by said magnet,
said magnet being housed in a first rotor part defining a first
pair of rotor poles, said excitation coil being housed in a second
rotor part defining a second pair of rotor poles, said first and
second rotor parts being separated from each other by essentially
magnetically non-conductive areas.
2. The machine according to claim 1, wherein said second rotor part
has a generally U-shape ferromagnetic part with two branches
defining said two poles and receiving said excitation coil.
3. The machine according to claim 2, wherein said second rotor part
has a single excitation coil around a base of said U-shape
ferromagnetic part joining said branches and adapted to create a
magnetic flux propagating the same way in a generally
circumferential direction as the magnetic flux generated by said
magnet.
4. The machine according to claim 2, wherein said second rotor part
has two excitation coils around said branches of said U-shape part
adapted to create magnetic fluxes of which one is directed towards
the inside and the other towards the outside of said rotor.
5. The machine according to claim 1, wherein said rotor has along
its periphery alternating first parts and second parts.
6. The machine according to claim 1, wherein said first rotor parts
each have two ferromagnetic parts on respective opposite sides of
the associated magnet.
7. The machine according to claim 6, wherein said ferromagnetic
parts of said first rotor parts form part of a single core.
8. The machine according to claim 1, wherein said magnetically
non-conductive areas comprise airgaps.
9. The machine according to claim 1, wherein said magnetically
non-conductive areas comprise a magnetically non-conductive
material.
10. The machine according to claim 1 comprising a motor vehicle
alternator.
11. The machine according to claim 9, wherein the non-conductive
material comprises a plastic material.
12. The machine according to claim 1, wherein each magnet is housed
in a respective first rotor part and each excitation coil is housed
in a respective second rotor part.
13. A motor vehicle including the machine according to claim 1.
14. An apparatus comprising:
a stator including at least one armature coil; and
a rotor to establish closed magnetic circuits around sections of
the armature, including:
at least one first pair of rotor poles, associated with a permanent
magnet, to establish a magnetic flux in a circumferential direction
of the rotor, and
at least one second pair of rotor poles, associated with an
excitation coil, to establish a variable magnetic flux in the same
circumferential direction as the flux produced by the permanent
magnet, the first and second pairs separated from each other by an
essentially magnetically non-conductive area.
15. The apparatus according to claim 14, wherein the non-conductive
area comprises an air gap.
16. The apparatus according to claim 15, wherein the rotor includes
a plurality of the first and second pairs of rotor poles
alternating along a periphery of the rotor.
17. The apparatus according to claim 14, wherein the rotor
comprises:
at least one first rotor part for housing the magnet to define the
first pair of rotor poles; and
at least one second rotor part for housing the excitation coil to
define the second pair of rotor poles.
18. The apparatus according to claim 17, wherein the second rotor
part comprises a generally U-shape ferromagnetic rotor part with
two branches defining two poles of the second rotor pair.
19. An apparatus comprising:
a stator including at least one armature coil; and
a rotor to establish closed magnetic circuits around sections of
the armature, including:
at least one first means for establishing a magnetic flux in a
circumferential direction of the rotor through the use of a
permanent magnet, and
at least one second means, separated from the first means by an
essentially magnetically non-conductive area, for establishing a
variable magnetic flux in the same circumferential direction as the
flux produced by the first means through the use of an excitation
coil.
20. The apparatus according to claim 19, wherein the rotor includes
a plurality of the first and second means alternating along a
periphery of the rotor.
Description
FIELD OF THE INVENTION
This invention relates to rotating machines such as motor vehicle
alternators.
BACKGROUND OF THE INVENTION
The single-phase or multiphase generator constituting the
conventional motor vehicle alternator generally has a stator within
which rotates a rotor carrying an excitation coil. The coil is
connected to brushes in contact with two slip rings on a projecting
part of the rotor shaft.
EP-A-0 707 374 discloses rotating machines in which, for improved
efficiency, the rotor excitation field is produced by permanent
magnets and by coils (the expression "mixed excitation" is
generally used), and in which the current delivered by the armature
is controlled by excitation coil switching means which selectively
reverse the excitation direction to reduce or even substantially
eliminate the flux from the magnets.
This need to reverse the direction of the excitation current
imposes the use of a so-called "H" semiconductor switching bridge,
which is costly and adds to the unit cost of the machine.
DISCUSSION OF THE INVENTION
An object of the invention is to overcome the above drawbacks and
to propose a machine, in particular a rotating machine such as an
alternator, with mixed excitation and in which the output current
can be regulated by varying unidirectional excitation by coils, and
in particular by varying excitation by coils between an essentially
zero value and a maximum value to deliver an energy varying in a
given range. Thus in particular the invention aims to provide mixed
excitation in situations that do not require an excitation varying
between a zero value and a maximum value but where an excitation
varying between a non-zero minimum value and a maximum value is
sufficient.
Another essential object of the invention, in a machine of the
above kind, is to reduce the number of magnets required for a given
number of rotor poles combined with comparable levels of excitation
by magnets and excitation by coils.
Accordingly the invention proposes a flux commutating electrical
machine including a stator and a rotor wherein the stator includes
at least one armature coil housed in at least one pair of notches,
the rotor includes means for selectively establishing closed
magnetic circuits around sections of the armature coil(s) including
at least one excitation permanent magnet adapted to establish a
magnetic flux in a circumferential direction of the rotor and at
least one excitation coil adapted to establish a localized variable
magnetic flux in the same circumferential direction as the flux
produced by the magnet (s), the magnet or each magnet is housed in
a first rotor part defining a first pair of rotor poles, the coil
is or the coils are housed in a second rotor part defining a second
pair of rotor poles and the rotor parts are separated from each
other by essentially magnetically non-conductive areas. The machine
in accordance with the invention has the following preferred but
non-limiting features:
the or each second rotor part has a generally U-shape ferromagnetic
part with two branches defining the two poles and receiving at
least one excitation coil.
the or each second rotor part has a single excitation coil around a
base of the U-shape part joining the branches and adapted to create
a magnetic flux propagating the same way in a generally
circumferential direction as the magnetic flux generated by the or
each magnet.
the or each second rotor part has two excitation coils around the
branches of the U-shape part adapted to create magnetic fluxes of
which one is directed towards the inside and the other towards the
outside of the rotor.
the rotor has along its periphery alternating first parts and
second parts.
the first rotor parts each have two ferromagnetic parts on
respective opposite sides of the associated magnet.
the ferromagnetic parts of the first rotor parts form part of a
single core.
the magnetically non-conductive areas are airgaps.
the magnetically non-conductive areas comprise a magnetically
non-conductive material such as a plastics material.
The invention further proposes a machine as defined hereinabove
constituting a motor vehicle alternator.
Other aspects, aims and advantages of the invention will appear
more clearly on reading the following detailed description of
preferred embodiments of the invention which is given by way of
non-limiting example only and with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a is a diagrammatic developed view of a rotor and stator
system of a rotating machine constituting a first embodiment of the
invention in a state of non-excitation of the field coils.
FIG. 1b is a view similar to FIG. 1a in a state of excitation of
the field coils.
FIG. 2 is a diagrammatic developed view of a rotor and stator
system of a rotating machine constituting a second embodiment of
the invention in a state of excitation of the field coils.
FIG. 3 is a diagrammatic view in cross-section of a concrete
embodiment of the core of a rotor and stator system conforming to
FIGS. 1a and 1b.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
Referring first to FIGS. 1a and 1b, there is shown diagrammatically
and in developed form part of a stator 1 and the corresponding part
of a rotor 2 of a single-phase or multiphase electrical machine in
accordance with the invention, such as an alternator.
The stator 1 has a core 12 defining a continuous annular structure
with a plurality of notches 13 on its inside periphery receiving
sections of armature coils 14 in a manner that in itself is
entirely conventional.
There is an even number of notches 13 which are equi-angularly
distributed, leaving poles 15 between them.
The rotor 2 is defined by a succession of magnetically separate
individual structures or cells. These structures comprise a U-shape
first ferromagnetic structure 21 with two branches 211, 212 the
free ends of which define two external projecting poles, the
angular pitch of which is equal to that of the poles 15 of the
rotor in the case of a single-phase machine, and a base 213.
An excitation coil 214 is wound around the base 213 and is
connected to an excitation voltage source (not shown) to generate
in it a magnetic flux from left to right as shown in FIGS. 1a and
1b.
A plurality of equi-angularly spaced U-shape structures as
described above is preferably provided.
Interleaved between the U-shape structures 21 are the same number
of permanent magnet structures 22 each comprising a permanent
magnet 225 trapped between two ferromagnetic members 221, 222 the
faces of which that face towards the stator constitute poles, the
poles of the U-shape structures 211 and those of the members 221,
222 being equi-angularly spaced around the outside periphery of the
rotor.
In the case of a three-phase machine the number of stator notches
13 is three times the number of rotor poles as defined
hereinabove.
The structures 21 and 22 are separated by gaps 30 extending
substantially the full height of the rotor (i.e. its axial
dimension in the case of a cylindrical rotor).
Clearly, given the above explanations, the various components of
the rotor can be provided in N sets disposed in successive groups,
according to the required number of poles.
The behavior of a rotating machine, in this instance an alternator,
the operating principle of which is as described hereinabove will
now be described with reference to FIGS. 1a and 1b.
Consider first the situation in which there is no excitation
current in the excitation coil 214 (FIG. 1a).
In this case a portion F1 of the magnetic flux generated by a
permanent magnet 225 can flow in a closed loop through the
associated members 221 and 222 and the stator 1, around a
respective armature section 14, to generate a minimum armature
current in the armature coil concerned.
Note also that another portion F2 of the flux produced collectively
by the magnets follows a sinuous path along the rotor, and this
flux F2 also contributes to generating a current in the armature
windings.
This situation is one of minimum excitation of the machine,
corresponding to the fluxes F1 and F2 generated by the magnets
225.
FIG. 1b shows the situation in which the excitation coils 214 of
the rotor carry an excitation current.
Each of the coils generates a first flux portion F3 that flows in a
closed loop around an associated armature coil section 14, in the
same direction as the flux F1 generated by the magnets 225 (here
from right to left in the stator 1).
The flux generated by the coils adds to the flux F2 described
hereinabove to form a higher flux F2' that also contributes to
increasing the armature current.
When the current in the excitation coils 214 is maximum there is
maximum transfer of energy to the stator.
Accordingly, by controlling a unidirectional current flowing in the
field coils 214 between a zero value and a maximum value a transfer
of energy to the stator is achieved that varies between a non-zero
minimum value and a maximum value.
The ratio between the minimum and maximum values can of course be
altered by altering the values of the magnetic fluxes generated by
the magnets 225 and by the coils 214, respectively.
This produces a machine in which, using a unidirectional excitation
current varying between zero and a predefined maximum value, an
excitation is obtained varying as a monotonous function of the
current in a given range.
It is therefore possible to dispense with any "H" electronic
switching bridge or the like which, in the prior art mixed
excitation machines, produces a bi-directional current according to
the required excitation. This significantly reduces the cost of the
switching means, which can comprise a single semiconductor
switching device.
Another embodiment of a rotor and stator system in accordance with
the invention will now be described with reference to FIG. 2.
It differs from that shown in FIGS. 1a and 1b in that each U-shaped
structure 21 no longer comprises a single coil 214 but instead two
coils 215, 216 around the respective branches 211 and 212 of the
U-shaped part.
Note that the dimension of the U-shaped structures 21 in the
heightwise direction in FIG. 2 (i.e. in the radial direction for a
cylindrical rotor) can be greater in this case, the space left free
for the lower section of the coils 214 in FIGS. 1a and 1b being
superfluous in this situation.
The coils 215 and 216 of the same cell are fed in series or in
parallel with a current the direction of which is such that the
coil 215 generates a downwards magnetic flux and the coil 216
generates an upwards magnetic flux.
The behavior of this embodiment in the absence of any excitation
current is identical to that shown in FIG. 1a and will not be
described again.
Its behavior with an excitation current is similar to that of
FIG.1b, and produces the same kinds of flux F1, F2' and F3. Also,
note that the leakage fluxes at the two coils 215, 216,
respectively designated F4 and F5, usefully contribute to the
transfer of energy to the stator, their path passing around
corresponding notches of the latter.
Clearly, in FIG. 1b, the leakage flux of the single coil 214,
around its lower section, would be lost.
This second embodiment therefore increases the efficiency of the
machine.
A concrete embodiment of a machine in accordance with the invention
will now be described with reference to FIG. 3.
The stator 1 is of a type that is conventional in itself and has 36
equi-angularly spaced notches housing the various three-phase coil
sections, arranged in a manner that is also conventional.
The rotor 2 has three U-shape coil cells 21 of the type shown in
FIGS. 1a and 1b alternating with three permanent magnet cells 22 to
define a rotor with 12 alternating N and S poles.
The magnet cell sections 221, 222 are combined in a single central
core of the rotor.
The U-shape parts 211, 212, 213 of the coil cells are magnetically
separated from the cells 22. In practice they can be joined to the
aforementioned core by appropriate amagnetic parts, not shown.
In this regard note that the concept of the gap 30 between the
adjacent cells is to be understood in the present context as a gap
assuring only very limited magnetic coupling between said cells. It
can therefore be an airgap or a gap partly or completely filled
with an amagnetic material, in particular a plastics material.
In an embodiment that is not shown the rotor 2 can be obtained by
assembling a plurality of alternating individual cells 21 and 22
using appropriate mechanical means. Of course, the present
invention is not limited to the embodiments described and shown and
the skilled person will know how to vary or modify them in any way
within the spirit of the invention.
In particular, any combination of magnet structures and coil
structures can be provided in the rotor, for example two coil
structures or more between each pair of magnet structures, or two
magnet structures or more between each pair of coil structures.
In this case the coils and magnets are oriented to preserve
alternating N and S poles at the periphery of the rotor.
Each magnet structure 22 can have two or more magnets, the fluxes
from which combine to obtain the required effect of a flux creating
adjacent N and S poles on the rotor.
* * * * *